gralloctypes operator== in android namespace.

These being global interacts badly with operators defined in the android
namespace external to classes. This is because once operator== functions
in the android namespace are found, operator== functions in the global
namespace won't be considered.

Bug: 147842528
Test: compiles when 'android' namespace operators are introduced
upstream.

Change-Id: I54f3098103cb3623df80c54343fbc44ddab6a33a